The present disclosure relates generally to adapter curbs for HVAC systems.
More particularly, the present disclosure relates to roof adapter curbs used to facilitate connection of a new heating, ventilation, and air conditioning (HVAC) unit to the footprint of an old HVAC unit on a rooftop of a building. When roof top units reach the end of their useful life, they must be replaced with new units. Since 12-15 years have elapsed since the old unit was manufactured, improvements have been made in HVAC unit design to improve efficiency, reduce cost, etc. Many times, these changes result in different interface requirements (footprints) to the curb, even if the old and the new units are manufactured by the same manufacturer. In some instances, they can be very different interface configurations. In these cases, the industry norm is to fabricate an “adapter curb” to match the existing unit/curb on the bottom and match the new unit/curb on the top. The frames for these adapter curbs are factory fabricated to the given specifications of a particular project and shipped to the job site. Most often, these curbs are shipped with loose items that are needed for installation but items that are required to be field installed in current designs.
In many installations, electrical connections and wiring for the old unit are often not readily connectable to the electrical connections and wiring of the new unit. In the best case, the new connection is directly above the old connection but the electrical services still must be extended upward to accommodate the height of the adaptor curb. In the worst case, the connections are diagonally opposite from each other and services must be extended internally or in some situations externally around the adaptor curb. Thus, the technicians must rout electrical, controls, fire, communication, etc. cables from the existing point of contact to a new connection location which can involve field installing junction boxes, drilling holes for conduit connectors, field fabricating conduit components, cutting to length and installing new cables, splicing cable connections to the old, etc. Most times this effort requires some of the work to be done below the roof once the adapter curb is positioned on the existing curb. Such work can require the use of ladders and/or lifts, and can be cumbersome for the field technician, thereby adding significant time and cost to the installation of the new unit. Experience has shown that up to 50% of the crew's time is spent field fabricating and extending service cables alone. In addition, this work requires significant raw inventory be carried to the job in case such materials are needed for connecting the old electrical wiring to the new.
Additionally, in some installations, gas piping must be run to the new HVAC unit during installation. Like electrical wiring, connection of gas piping to the new HVAC unit can require a field technicians to spend time beneath the roof to run the existing piping up through the adapter curb and to the new HVAC unit, and can also include installing extension gas piping to connect to appropriate locations on the new HVAC unit.
Additionally, in many installations, sealing materials, such as top and bottom seals between the adapter curb and the new unit and existing curb, respectively, are installed on-site, as well as insulation materials on the interior walls of the adapter curb. This is a laborious and time consuming task. Once the old unit has been removed from the original curb, the installation crew cleans the mating surface and installs a new seal on the curb before installing the adapter curb on top of the original curb. This is typically accomplished with rolls of adhesive backed foam (neoprene) or similar material. If the weather is damp or wet, it is difficult to get the seal to stick and stay in position during the installation process, thereby leading to unwanted and expensive air leaks. This same problem occurs with the seal which is field applied to the top of the adapter curb. The sealing material can also produce significant waste materials, such as paper backings for the sealing materials, which can increase the clean-up of the installation site. Such materials can also be blown around or off of a roof or building site undesirably, creating more work for the installation crew in cleaning up the job site.
Once the adapter curb and new rooftop unit have been properly placed, code requires that the components be secured to the structure below in order to survive anticipated wind and seismic loading. Customarily, curb manufacturers provide “wind brackets” or “hurricane brackets” as lose items to be field installed on an upper end of the adapter curb to secure the new unit to the adapter curb. Further, curb manufacturers sometimes provide installation instructions for how the adapter curb is to be secured to the existing curb, typically by screwing the lower end of the adapter to the existing curb. Often this crucial part of the installation is left up to the discretion of the installation technicians (number of screws, spacing of screws, screw sizing, etc.) and may or may not be sufficient to handle the design loads.
The deficiencies in conventional adapter curbs discussed above can generally increase installation time and costs at a work site, which is undesirable. Additionally, adapter curbs and HVAC units often weigh hundreds of pounds and thus mechanical lifting is required via a crane or other lifting device during installation. Longer installation times can increase the amount of time the lifting equipment needs to be used and/or rented which can also significantly increase costs of installation.
What is needed then are improvements to roof adapter curbs for HVAC systems.